The proposed experiments are designed to study te mechanism of neural excitation in the cochlea, with emphasis on elucidating the role of cochlear microphonics (CM), the summating potential (SP), and the endocochlear potential (EP). The proposed experiments involve the simultaneous recording of cochlear potentials and neural responses in gerbils and guinea pigs. The potentials will be modified by the application of extrinsic current or low-frequency acoustic stimuli, and the changes in EP, CM, and SP will be quantitatively compared with the changes in neural response. Measurement of whole nerve responses (N1) to the same stimuli will be used to supplement the single-fiber data. The resulting data will be used to elucidate the coupled role of inner and outer hair cells in the process of neural excitation. Comparative studies will be made on the neural excitation process in the hair-cell system of the lateral-line organ of the African clawed toad Xenopus laevis. The effects of electric potentials upon spontaneous and evoked neural activity and the effects of the ionic composition of the surrounding fluids will be investigated. Theoretical modeling of cochlear function incorporating experimental data will complement the experimental studies.